Ink jet ink comprising encapsulated pigment dispersions with minimal free polymer

ABSTRACT

The present disclosure provides an inkjet ink comprising an aqueous vehicle and an encapsulated pigment dispersion. A process for encapsulating pigment dispersions is provided where a pigment is dispersed with a polymeric dispersant in an aqueous solvent system. The free polymer dispersant in the pigment dispersion is limited to less than 0.12 grams per gram of pigment. This dispersed pigment is then encapsulated by adding acrylate monomers and optionally acrylic and vinyl monomers and polymerizing. In the encapsulated pigment dispersion the weight ratio of final free polymer to polymer found to the final encapsulated pigment is less than 0.9. The free polymer dispersant is measured by a centrifugation method and the final free polymer is measured by a density gradient centrifugation method. Such encapsulated pigment dispersions may be used in inkjet inks and are stable to heat, aging test conditions, and solvent challenges. Prints from these inks have better durability.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 from U.S.Provisional Application Ser. No. 61/507,756, filed Jul. 14, 2011 whichis incorporated by reference in its entirety.

BACKGROUND OF THE DISCLOSURE

The present disclosure pertains to aqueous inkjet inks which comprise anaqueous vehicle and an encapsulated pigment dispersion as the colorant.More particularly, the disclosure relates to a dispersion process wherea dispersed pigment is prepared with the amount of polymeric dispersantthat is not bound to the pigment minimized, then monomers are added tothe dispersed pigment, and polymerization is initiated to obtain anencapsulated pigment which has minimal free polymer in the finalencapsulated pigment dispersion.

Dispersion methods are commonly used to disperse particles. A variety ofdispersion processes have been described for dispersing particles. Forinkjet inks pigments are dispersed with polymeric dispersants. Recently,processes have been described where the polymeric dispersed pigments aresubject to a process that results in encapsulated pigments.

In U.S. Pat. No. 6,262,152 describes preparing encapsulated pigmentswhere the encapsulation is achieved by using polymeric dispersants whichhave reactive sites and adding monomers that have substituents that canreact with the reactive sites of the polymeric dispersant. For instance,the dispersant has isocyanate reactive groups and an isocyanate is addedto react with the polymeric dispersant.

U.S. Pat. No. 7,612,124 describes polymer-enclosed color-impartingparticles that are enclosed by a friable polymer formed from awater-dispersible polymerizable material.

U.S. Pat. No. 7,741,384 describes an encapsulation process where boththe pigment dispersion and the monomer dispersion are separately mixedutilizing a surfactant to independently stabilize the dispersion and themonomer.

US Patent Application Publication No. 200700227401 describes anencapsulation process where the monomer is stabilized via a miniemulsionwhich is stabilized by a hydrophobic organic compound.

US Patent Application Publication No. 20080064786 describes a waterinsoluble polymeric dispersant for the pigment and two crosslinkingsteps, the first occurring in a ketone/water solvent and crosslinks thecore of the polymer followed by a second crosslinking for the shell ofthe polymer.

There have been efforts in the art directed at improving the stabilityof pigment dispersions. These efforts have included improvements in theprocesses used to make the dispersions, the development of newdispersants and the exploration of the interaction between dispersantsand pigment particles, and between dispersants and the aqueous vehicle.While much of the effort has general application at improving dispersionstability, some of that effort has not found utility in particularapplications. For example, the pigment dispersions used in inkjetprinting applications have very unique and demanding requirements. It iscritical that ink components comprising pigment dispersion remainstable, not only in storage but also over repeated jetting cycles. It isalso desirable that the pigment dispersions offer good durability, goodrub-fastness, wet-fastness and highlighter pen fastness. As the inkjetindustry moves to page-wide array printing the requirements forrepeating jetting cycles may be an order of magnitude higher than thetraditional Small Office/Home Office market. These and other emergingneeds require improved pigment dispersions.

A need exists for highly stable, higher-quality and different propertyinks for ink-jet applications. Although improvements in polymericdispersants have significantly contributed to improved ink-jet inks, thecurrent dispersants still do not provide inks with the requisitestability, durability, optical density and chromaneeded for inkjetapplications. The present invention satisfies this need by providing anencapsulated pigment dispersion based on a pigment which is stabilizedby a polymeric dispersant to which is added acrylate monomers andoptionally acrylic or vinyl monomers, which are, in turn, polymerized.This results in an encapsulated pigment dispersion that has morestability, better jetting without compromise of color properties andmore flexibility for ink formulation.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to encapsulating pigments for use ininkjet inks which have low free polymer in the dispersion of theencapsulated pigment. The encapsulation is achieved by polymerizingmonomers in the presence of polymerically dispersed pigments. After thedispersion of the pigment the free polymer in the initial pigmentdispersion is less than 0.1 grams per gram of pigment as measured by acentrifugation method. Then acrylate, optional acrylic monomers and/orvinyl monomers are added and these monomers are polymerized toencapsulate the pigment. In the final encapsulated pigment dispersionwhere the weight ratio of free polymer to polymer bound to the pigmentis less than 0.9 as measured by a density gradient centrifugationmethod.

Accordingly,

A method of making an encapsulated pigment dispersion comprising stepsof

-   -   a) dispersing a pigment using a polymeric dispersant in an        aqueous vehicle wherein the polymeric dispersant not bound to        the pigment is less than 0.12 grams per gram of pigment in the        pigment dispersion and the polymer dispersant bound to the        pigment is less than 0.33 grams per gram of pigment where the        polymeric dispersant not bound to the pigment is measured by a        centrifugation method;    -   b) adding at least one encapsulation monomer to the aqueous        vehicle of step (a) to form a first dispersed        pigment/encapsulation monomer/aqueous mixture and wherein the        encapsulation monomer comprises acrylate monomers;    -   c) dispersing the encapsulation monomer/aqueous mixture using        high shear mixing to form a second dispersed        pigment/encapsulation monomer/aqueous mixture;    -   d) polymerizing the encapsulation monomer by adding a        polymerization initiator to the second dispersed        pigment/encapsulation monomer/aqueous mixture wherein for the        final encapsulated pigment dispersion the weight ratio of final        free polymer to bound polymer is less than 0.9 and where the        final free polymer is measured by a density gradient        centrifugation method.

The polymeric dispersants that can be used for dispersing the pigmentsare random or structured polymers commonly used for inkjet ink pigmentsand can be based acrylate/acrylic monomers or polyurethanes. Thepolymeric dispersant for dispersing the pigments can be neutralizedprior to, during or after the start of the dispersion process.

Additional monomers may be added prior to the polymerization step. Theseadditional monomers may include acrylic monomers, acrylate monomers withnonionic components, vinyl acetate, styrene and other monomers thatcontain polymerizable double bonds and di- or tri-acrylates.

In accordance with another embodiment, there is provided an aqueouspigmented inkjet ink comprising an aqueous encapsulated pigmentdispersion as described above. The pigment inkjet ink has from 0.1 to 15wt % pigment based on the total weight of the ink, a surface tension inthe range of 20 dyne/cm to 70 dyne/cm at 25° C., and a viscosity oflower than 30 cP at 25° C.

In still another embodiment, there is provided an ink set comprising atleast one cyan ink, at least one magenta ink and at least one yellowink, wherein at least one of the inks is an aqueous encapsulatedpigmented inkjet ink as set forth above and described in further detailbelow. This ink set is often described as a CMY ink set.

In still another embodiment, there is provided an ink set comprising atleast one cyan ink, at least one magenta ink, at least one yellow ink,and at least one black ink wherein at least one of the inks is anaqueous encapsulated pigmented inkjet ink as set forth above anddescribed in further detail below. This ink set is often described as aCMYK ink set.

Other ink sets may include additional colors, as long as at least one ofthe inks is an aqueous encapsulated pigmented inkjet ink as set forthabove and described in further detail below.

In yet another embodiment there is provided a method for inkjet printingonto a substrate, comprising the steps of:

-   -   (a) providing an inkjet printer that is responsive to digital        data signals;    -   (b) loading the printer with a substrate to be printed;    -   (c) loading the printer with an ink as set forth above and        described in further detail below, or an inkjet ink set as set        forth above and described in further detail below; and    -   (d) printing onto the substrate using the ink or inkjet ink set        in response to the digital data signals.

These and other features and advantages of the present invention will bemore readily understood by those of ordinary skill in the art from areading of the following Detailed Description. One of skill canappreciate that certain features of the invention which are, forclarity, described above and below in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the invention that are, for claritydescribed above and below as a a single embodiment, may also be providedseparately or in an embodiment. In addition, references in the singularmay also include the plural (for example, “a” and “an” may refer to one,or one or more) unless the context specifically states otherwise.Further, references to values stated in ranges include each and everyvalue within that range.

DETAILED DESCRIPTION

Unless otherwise stated or defined, all technical and scientific termsused herein have commonly understood meanings by one of ordinary skillin the art to which this invention pertains.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight. When an amount, concentration, or other value or parameter isgiven as either a range, preferred range or a list of upper preferablevalues and lower preferable values, this is to be understood asspecifically disclosing all ranges formed from any pair of any upperrange limit or preferred value and any lower range limit or preferredvalue, regardless of whether ranges are separately disclosed. Where arange of numerical values is recited herein, unless otherwise stated,the range is intended to include the endpoints thereof, and all integersand fractions within the range.

Unless it is otherwise stated or clear from the context, when discussingproperties or components of an inkjet ink, the term “inkjet ink” may beunderstood to include inkjet ink sets.

When the term “about” is used in describing a value or an end-point of arange, the disclosure should be understood to include the specific valueor end-point referred to.

As used herein, “comprising” is to be interpreted as specifying thepresence of the stated features, integers, steps, or components asreferred to, but does not preclude the presence or addition of one ormore features, integers, steps, or components, or groups thereof.Additionally, the term “comprising” is intended to include examplesencompassed by the terms “consisting essentially of” and “consistingof:” Similarly, the term “consisting essentially of” is intended toinclude examples encompassed by the term “consisting of:”

As used herein, the term “dispersion” means a two phase system where onephase consists of finely divided particles (often in the colloidal sizerange) distributed throughout a bulk substance, the particles being thedispersed or internal phase and the bulk substance the continuous orexternal phase. The bulk system is often an aqueous system.

As used herein, the term “dispersion of pigment particles” is a stabledispersion of polymeric dispersed pigments which are normally used ininks and paints.

As used herein, the term “aqueous pigment dispersion” is an aqueousdispersion of pigments using polymeric dispersants.

As used herein, the term “dispersant” means a surface active agent addedto a suspending medium to promote uniform and maximum separation ofextremely fine solid particles often of colloidal size. For pigments,the dispersants are most often polymeric dispersants and usually thedispersants and pigments are combined using dispersing equipment.

As used herein, the term “structured polymer” means a polymer that iscomposed of segments that differ in composition from each other.Examples include diblock, triblock, graft and star polymers.

As used herein, the term “random polymer” means a polymer that iscomposed of monomers distributed in a random fashion in the polymer inmuch the same mole ratio of the monomers in the initial monomercomposition.

As used herein, the term “ionically stabilized dispersions”, (“ISD”) arepolymerically stabilized dispersions where the stabilization is due toionic stabilization with little or no steric stabilization.

As used herein, the term “dispersible particles” are those particlesthat can be dispersed with dispersants including polymeric dispersants.

As used herein, the term “stable dispersion” means a particle dispersionwhere the particle size growth is less than 10% particle size growth andno flocculation when the dispersion is stored at room temperature for atleast a week.

As used herein, the term “pigment” means any substance usually in apowder form which imparts color to another substance or mixture.Disperse dyes, white and black pigments are included in this definition.

As used herein, the term “P/D” means the pigment to dispersant weightratio in the initial dispersion formulation.

As used herein, the term “drop” means a drop of liquid that is normallyobtained from a laboratory dropper at room temperature and is normallyabout 0.04 grams for aqueous systems.

As used herein, the term “ambient conditions” refers to surroundingconditions, which are often around one atmosphere of pressure, about 50%relative humidity, and about 25° C.

As used herein, the term “encapsulation” means to encase a pigment in apolymeric system where the polymeric system is a product of polymerizingmonomers in the presence of a pigment which is dispersed with apolymeric dispersant.

As used herein, the term “crosslinking” means the chemical reactionbetween reactive groups on at least two different chemicals, where oneof the chemicals is at least disubstituted.

As used herein, the term “emulsion” means a stable mixture of two ormore immiscible liquids held in suspension by small percentages ofsubstances called emulsifiers.

As used herein, the term “miniemulsion” means dispersions of relativelystable oil droplets with a size in the 50 to 500 nanometer regionprepared by shearing a system containing an oil, water, and asurfactant.

As used herein, the term “nonionic” means an oligomer or polymer derivedfrom ethylene oxide and/or propylene oxide where there are at least 4 ofthe ethylene oxide or propylene oxide groups.

As used herein, the term “binder” means a film forming ingredient in theinkjet ink. This binder is normally added when the ink is formulated.

As used herein, the term “HSD” means High Speed Dispersing.

As used herein, the term “OD” means optical density.

As used herein, the term “Gloss” means observation of reflected lightfrom a printed surface, normally the printed substrate is glossy paper.

As used herein, the term “SDP” means self-dispersible” “self-dispersing”or “self-dispersed” pigments.

As used herein, the term “free polymeric dispersant”, means thepolymeric dispersant which is unbound to the pigment, and can bedetermined by centrifugation method.

As used herein, the term “bound polymer dispersant”, means the polymericdispersant which is bound to the pigment or associated with the pigment,and is the difference between the total polymeric dispersant and thefree polymeric dispersant.

As used herein, the term “free polymer”, means the polymer which isunbound to the pigment after the final encapsulated pigment step, andcan be determined by the gradient density centrifugation method.

As used herein, the term “aqueous vehicle” refers to water or a mixtureof water and at least one water-soluble organic solvent (co-solvent).

As used herein, the term “ionizable groups”, means potentially ionicgroups.

As used herein, the term “substantially” means being of considerabledegree, almost all.

As used herein, the term “Mn” means number average molecular weightusually reported in daltons.

As used herein, the term “Mw” means weight average molecular weightusually reported in daltons.

As used herein, the term “Pd” means the polydispersity which is theweight average molecular weight divided by the number average molecularweight.

As used herein, the term “D50” means the particle size at which 50% ofthe particles are smaller; “D95” means the particle size at which 95% ofthe particles are smaller.

As used herein, the term “cP” means centipoise, a viscosity unit.

As used herein, the term “conductivity” means the property of asubstance or mixture that describes its ability to transfer electricityand is reported as mS/cm.

As used herein, the term “pre-polymer” means the polymer that is anintermediate in a polymerization process, and can also be considered apolymer.

As used herein, the term “AN” means acid number, mg KOH/gram of solidpolymer.

As used herein, the term “neutralizing agents” means to embrace alltypes of agents that are useful for converting ionizable groups to themore hydrophilic ionic (salt) groups.

As used herein, the term “PUD” means the polyurethane dispersionsdescribed herein.

As used herein, the term “GPC” means gel permeation chromatography.

As used herein, the term “ETEGMA//BZMA//MAA” means the block copolymerof ethoxytriethyleneglycol methacrylate, benzylmethacrylate andmethacrylic acid.

As used herein, the term “NMP” means n-Methyl pyrrolidone.

As used herein, the term “THF” means tetrahydrofuran.

As used herein, the term “Tetraglyme” means Tetraethylene glycoldimethyl ether.

As used herein, the term “Vazo® 68” refers to a free radical source forpolymerization; the product is obtained from DuPont, Wilmington Del.

As used herein, the term “Liponics EG-1” refers to a humectant obtainedfrom Lipo Chemicals, Paterson, N.J.

As used herein, the term “PROXEL™ biocide” refers to a biocide obtainedfrom Arch Chemicals, Norwalk, Conn.

As used herein, the term “Desmophen® 1200” refers to a slightlybranched, hydroxyl-bearing polyester obtained from Bayer MaterialScience, Pittsburgh, Pa.

Unless otherwise noted, the above chemicals were obtained from Aldrich(Milwaukee, Wis.) or other similar suppliers of laboratory chemicals.

Encapsulation Description

There are at least four distinct steps to the method of making theencapsulated pigments with low final free polymer.

-   -   a) Disperse a pigment with a polymeric dispersant in an aqueous        vehicle. After the dispersion step the polymeric dispersant is        associated with the pigment or is dissolved or dispersed in the        aqueous vehicle. The means of dispersing the pigment are chosen        to minimize the free polymeric dispersant, or after the        dispersion the pigment dispersion is purified to remove excess        free polymeric dispersant. The amount of free polymer dispersant        is less than 0.12 gram/gram of pigment as measured by the        centrifugation method. The amount of polymer dispersant bound to        the pigment is less than 0.33 grams per gram of pigment.    -   b) Add at least one acrylate monomer to the pigment dispersion        from (a). Other optional monomers may be added which include        acrylics and vinyl compounds.    -   c) Mix the acrylate with the dispersed pigment using high shear        mixing to form a mixture of monomers and the dispersed pigment.    -   d) Polymerize the monomers by adding a polymerization initiator        which results in a final encapsulated pigment where the weight        ratio of free polymer to polymer bound to the pigment is less        than 0.9. as measured by the density gradient centrifugation        method.

The free polymeric dispersant of step (a) is determined by thecentrifugation method. “Free polymer”, that which is unbound to thepigment in the pigment dispersion, is determined from the gravimetric %solids of the supernatant of the sample, after the pigment is removed bycentrifugation.

1. The pigment dispersion sample is diluted with deionized water to 5%pigment.

2. The diluted sample is centrifuged at 20,000 rpm for 2 hours.

3. The pigment-free supernatant is analyzed for % solids content

The amount of bound polymeric dispersant is defined as the differencebetween the initial amount of polymeric dispersant and the free polymerdispersant from the centrifugation method.

The free polymer in the encapsulated pigment mixture is determined by adensity gradient method:

-   -   1. Add 75/25 Glycerol water solution to each centrifuge tube        (approx. ⅓ of tube volume, ˜11-12 g)    -   2. Slowly add 10.0 grams of the 5% pigment dispersion to be        tested. Add by letting the dispersion slowly drain down the side        of the tube to layer the dispersion on the top of the glycerol        solution.    -   3. Centrifuge two hours at 25 degrees C. and 50,000 RPM    -   4. Carefully withdraw top layer containing polymer using the        high intensity light and a long glass pipette and place into a        tared aluminum weigh dish.    -   5. Bake for 3 to 4 hours in 95 deg C. convection oven to remove        water and then transfer to a 150 deg C. vac. oven until dry        (overnight).        The free polymer is the amount of polymer found in the        supernatant. The amount of bound polymer is defined as the        difference between the sum of the initial amount of polymeric        dispersant and added monomers and the free polymer from the        density gradient centrifugation method.

The free polymer at step 1 is constrained to be less than 0.12 g of freepolymer per gram of pigment. This may be achieved by the selection ofthe dispersion process or by purification of the pigment dispersionprior to adding the monomers of step (b). Non-limiting examples ofdispersion methods that can result in lower free polymeric dispersantsinclude initially using solvents during the dispersion process prior toadding the aqueous vehicle. A dispersion can be made in solvent, thesolvent removed and the system converted to an aqueous one. Anothersimilar method is to start with a solvent system and add a more polarsolvent such as water during the dispersion process to significantlychange the polarity of the dispersion media. Non-limiting examples ofpurification means are to ultrafilter the pigment dispersion to removefree polymer dispersant below the 0.12 gram limit of free polymericdispersant. Alternatively the free polymer dispersant may be below 0.1 gof free polymer dispersant per gram of pigment.

The polymeric dispersant which is bound to the pigment is less than 0.33grams per gram of pigment. The bound polymeric dispersant is thedifference between the total mass of the polymeric dispersant and thefree polymeric dispersant as measured by the centrifugation method.Alternatively, the polymeric dispersant which is bound to the pigment isless than 0.25 grams per gram of pigment.

The free polymer after the encapsulation step must be below a 0.9 weightratio of free polymer to polymer associated with the pigment in thefinal encapsulated pigment as measured by the density gradientcentrifugation method. While not wishing to be bound by theory it isbelieved that the free polymer is a combination of polymeric dispersantand monomers that were polymerized and are not associated with thepigment.

The bound polymer is that polymer which is associated with the pigment.It is a combination of the initial polymeric dispersant and thepolymerized monomer. It is thought that the bound polymer bothstabilizes the pigment and when the encapsulated pigment is used in aninkjet ink the bound polymer helps keep the pigment on or near thesurface of the printed substrate when the pigment dispersion is used inan inkjet ink. As such the resulting print is much more durable thanwhen the pigment has not been encapsulated in this manner.

The limitation of the weight ratio of 0.9 free polymer to bound polymercan lead to better properties of the encapsulated pigment and, in turn,an inkjet ink that has better performance. The better properties caninclude stability to high temperature testing, formulation latitude whenthe encapsulated pigments are used in subsequent uses. In the case wherethe subsequent use is in an inkjet ink better print performance isobserved which includes larger volumes of ink successfully put throughan inkjet printhead. Alternatively, the weight ratio of free polymer tobound polymer may be less than 0.75 and further less than 0.6.

Each of the components of the encapsulated pigment system will bedescribed.

Pigments

Pigments suitable for use in the present invention are those generallywell known in the art for aqueous inkjet inks. Representative commercialdry pigments are listed in U.S. Pat. No. 5,085,698. Dispersed dyes arealso considered pigments as they are insoluble in the aqueous inks usedherein.

A wide variety of organic and inorganic pigments, alone or incombination, may be selected to make the ink. The term “pigment” as usedherein means an insoluble colorant which includes dispersed dyes as theyare insoluble in the inkjet ink. The pigment particles are sufficientlysmall to permit free flow of the ink through the inkjet printing device,especially at the ejecting nozzles that usually have a diameter rangingfrom about 10 micron to about 50 micron. The particle size also has aninfluence on the pigment dispersion stability, which is criticalthroughout the life of the ink. Brownian motion of minute particles willhelp prevent the particles from flocculation. It is also desirable touse small particles for maximum color strength and gloss. The range ofuseful particle size is typically about 0.005 micron to about 15 micron,and in embodiments, the pigment particle size range from about 0.005 toabout 5 micron, and in embodiments, from about 0.005 to about 1 micron.The average particle size as measured by dynamic light scattering ispreferably less than about 500 nm, more preferably less than about 300nm.

The selected pigment(s) may be used in dry or wet form. For example,pigments are usually manufactured in aqueous media and the resultingpigment is obtained as water-wet presscake. In presscake form, thepigment is not agglomerated to the extent that it is in dry form. Thus,pigments in water-wet presscake form do not require as muchdeflocculation in the process of preparing the inks as pigments in dryform.

The dispersed pigment may be purified after the dispersion process byfiltration, ultrafiltration or other processes used for purification ofdispersed pigments.

Polymeric Dispersants

Polymeric dispersants are those typically used for dispersing pigments,especially when these pigments are used for inkjet inks. Examples ofthese dispersants include polyurethanes and acrylic/acrylate copolymers.The polymers may be random or structured. The polymeric dispersant has anumber average molecular weight of 2000 to 9500 daltons. Optionally, themolecular weight is 2000 to 6000 daltons.

The structured polymeric dispersant may be water soluble and may have asolubility of at least 10 grams of polymer/100 grams of water at 25° C.The solubility is measured in its neutralized form.

A subset of the random and structured polymer dispersants are ionicallystabilized dispersants where the stabilization by the dispersant isionic with little or any steric stabilization. These ionic polymericdispersants were described in US Patent Application Publication No.20050090599.

The polymeric dispersant for the pigment may be either a random orstructured polymer. The polymer dispersant can be a copolymer ofhydrophobic and hydrophilic monomers. The hydrophobic monomers areacrylates and the hydrophilic monomers are acrylics. Alternately, thepolymeric dispersant may be a polyurethane.

Typical random polymeric dispersants have been described in U.S. Pat.No. 4,597,794.

The “structured polymer” can mean polymers having a block, branched,graft or star structure. Examples of structured polymers include AB orBAB block copolymers such as disclosed in U.S. Pat. No. 5,085,698; ABCblock copolymers such as disclosed in EP Patent Specification No.0556649; and graft polymers such as disclosed in U.S. Pat. No.5,231,131. Other polymeric dispersants that can be used are described,for example, in U.S. Pat. No. 6,117,921, U.S. Pat. No. 6,262,152, U.S.Pat. No. 6,306,994 and U.S. Pat. No. 6,433,117.

Polymer dispersants suitable for use in the present invention generallycomprise both hydrophobic and hydrophilic monomers. Some examples ofhydrophobic monomers used in random polymers are methyl methacrylate,n-butyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate,2-phenylethyl methacrylate and the corresponding acrylates. Examples ofhydrophilic monomers are methacrylic acid, acrylic acid,dimethylaminoethyl(meth)acrylate and salts thereof. Also quaternarysalts of dimethylaminoethyl(meth)acrylate may be employed.

Generally speaking the hydrophobic region is the part that contains theabsorbing segment, which is the segment or function of the dispersantinteracting with the pigment surface to effect dispersion. Thehydrophilic segment is the segment that provides the stability ofdispersion by interaction in the solute mixture to providestabilization. This stabilization is characterized as stericstabilization or ionic stabilization. These phenomena were described byH Spinelli in Adv. Mater, 1998, 10, no. 15, page 1215 to 1218. Theionically stabilized polymeric dispersants described above have littleif any steric stabilization.

The polymeric dispersant can be neutralized prior to the start of thedispersion process. That is, the initial mixture of solvent blend andpolymer dispersant has an appropriate amount of neutralizing agent.Alternatively, the neutralizing agent may be added with the polarsolvent during the dispersing process. An additional option is to havethe polymeric dispersant partially neutralized in the initial mixtureand add additional neutralizing agent in the polar solvent. The amountof neutralization of the polymeric dispersant in the final mixture is upto about 100% neutralized, and preferably up to about 90% neutralized.

The neutralizing agent can be hydroxides of the alkali metals, aminesand the like. Examples of neutralizing agents include organic bases suchas mono-, di, tri-methylamine, morpholine, n-methyl morpholine; alcoholamines such as dimethylethanolamine (DMEA), methyldiethanolamine, mono-,di, and tri-ethanolamine; pyridine; ammonium hydroxide;tetra-alkylammonium salts such as tetramethylammonium hydroxide,tetraethyl-ammonium hydroxide; alkali metals such as lithium, sodium andpotassium, and the like. Preferred neutralizing agents includedimethylethanolamine and sodium and potassium hydroxides, with potassiumhydroxide being particularly preferred for inks to be used in thermalinkjet printers.

The polyurethane polymeric dispersants are prepared from isocyanatescompounds, isocyanate-reactive compounds and a isocyanate or isocyanatereactive compound that has an ionic substituent. This ionic substituentis present in the polyurethane dispersant to stabilize it in an aqueoussolution. Often these polyurethane dispersants are prepared as apolyurethane prepolymer with excess isocyanate groups. Then a chainterminating isocyanate-reactive group is added to obtain polyurethanedispersant. The ionic content of the polyurethane can be as low as 10and as high as 90 milliequivalents/gram when measured as an acid groupor an amine group depending on the source of the ionic substituent. Theionic component is at least partially neutralized prior to its use as adispersant. The molecular weight range of these polyurethanes is from2000 to 9500 daltons.

Dispersion of the Pigment Particles

The dispersing step for the polymerically dispersed pigment may beaccomplished in an ultrasonicator, media mill, a horizontal mini mill,an attritor, or by passing the mixture through a plurality of nozzleswithin a liquid jet interaction chamber at a liquid pressure of at least5,000 psi to produce a uniform dispersion of the pigment particles inthe aqueous carrier medium (microfluidizer). The media for the mediamill is chosen from commonly available media, including zirconia, YTZ,and nylon. The media can be as small as about 0.1 microns, althoughparticles larger than 0.3 microns are commonly used. These variousdispersion processes are in a general sense well known in the art, asexemplified by U.S. Pat. Nos. 5,022,592, 5,026,427, 5,891,231,5,679,138, 5,976,232 and US Patent Application Publication No.20030089277. Preferred are media mill, and by-passing the mixturethrough a plurality of nozzles within a liquid jet interaction chamberat a liquid pressure of at least 5,000 psi. The mixing intensityrequired for the process is mixing normally associated with dispersionprocesses and not turbulent mixing of more modest mixing processes.

Combinations of dispersing equipment may be used. It may be moreconvenient to mix the solvent mixture, particle and polymeric dispersantin a High Speed Disperser (HSD) followed by milling in a media mill or amicrofluidizer. The addition of the polar solvent may occur during theHSD portion of the processing and then the milling is continued in themedia mill.

The final use of the particle dispersion may require that the solvent beremoved from the particle dispersion mixture. The solvent may be removedby distillation processing, ultrafiltration or other convenient means.Any of these solvent removal methods may be incorporated into theprocess. The dispersing equipment and the solvent removal may be coupledand the solvent may be removed during the dispersing process and duringthe addition of the polar solvent.

One way to monitor the progress of the dispersion process is to measurethe particle size and set a target value for the final D50 of themixture. For typical pigments used for ink-jet inks the target value ofthe D50 is 125 nm or less, preferably less than 100 nm. Also the D95 andthe particles smaller than 204 nm can be used as a test criterion forthe pigment dispersions.

A wide variety of organic and inorganic pigments, alone or incombination, may be selected for dispersion by this process. Thedispersed pigment may be used in paints, inks and especially inkjetinks. The term “pigment” as used herein means an insoluble colorant andin the present application includes disperse dyes. The pigment particlesare sufficiently small to permit free flow of the ink through the inkjetprinting device, especially at the ejecting nozzles that usually have adiameter ranging from about 10 micron to about 50 micron. The particlesize also has an influence on the pigment dispersion stability, which iscritical throughout the life of the ink. Brownian motion of minuteparticles will help prevent the particles from flocculation. It is alsodesirable to use small particles for maximum color strength and gloss.

The dispersed pigment may be purified after the dispersion process byfiltration, ultrafiltration or other processes used for purification ofdispersed pigments.

Crosslinked Polymeric Dispersant

The polymeric dispersant may be crosslinked after the pigment dispersionis prepared. This crosslinking step falls after Step (a) and before Step(b) in the method described above.

For crosslinking the polymeric dispersant is substituted withcrosslinkable moieties which are selected from the group consisting ofacetoacetoxy, acid, amine, epoxy, hydroxyl, blocked isocyanates andmixtures thereof. Then a crosslinking agent is added and thecrosslinking of the polymeric dispersant occurs. The crosslinking agentis selected from a group consisting of acetoacetoxy, acid, amine,anhydride, epoxy, hydroxyl, isocyanates, blocked isocyanates andmixtures thereof. The crosslinking of the polymeric dispersant is doneafter the pigment is dispersed and before the encapsulation monomer isadded. After the crosslinking step excess polymer can be removed bypurification processes such as ultrafiltration.

Specific examples of crosslinking moiety/agent pairs arehydroxyl/isocyanate and acid/epoxy.

Monomers for Encapsulation

The monomers used for the encapsulation are acrylates and, optionallyacrylics and other vinyl compounds. The acrylates are hydrophobicmonomers and in general include, for example, benzyl methacrylate, butylmethacrylate, methyl methacrylate, ethyl methacrylate, propylmethacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octylmethacrylate, lauryl methacrylate, stearyl methacrylate, phenylmethacrylate, phenoxyethyl methacrylate, methacrylonitrile, glycidylmethacrylate, p-tolyl methacrylate, sorbyl methacrylate, methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexylacrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate,stearyl acrylate, phenyl acrylate, phenoxyethyl acrylate, glycidylacrylate, p-tolyl acrylate, sorbyl acrylate, ethoxytriethyleneglycolmethacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate,2-ethoxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropylacrylate, di- and tri-methacrylates, and mixtures thereof.

Acrylic hydrophilic monomers can also be used as a monomer for theencapsulation. The amount of acrylic monomer is less than 20 weightpercent of the acrylates. Hydrophilic monomers include, for example,methacrylic acid, acrylic acid, maleic acid, maleic acid monoester,itaconic acid, itaconic acid monoester, crotonic acid, crotonic acidmonoester, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethylmethacrylate, N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethylacrylate, t-butylaminoethyl methacrylate, t-butylaminoethyl acrylate andmixtures thereof.

Acrylates with nonionic substituents may be included in the hydrophobicacrylate monomers. These nonionic components can be derived fromethylene oxide and propylene oxide and usually there are more than 3 ofthe ethylene oxide and propylene oxide groups. The total weight of thesenonionic substituents is less than 20 weight percent based on theacrylates.

Other monomers may be used such as styrene, alpha-methyl styrene,substituted styrenes, N-alkyl acrylamides, N-alkyl methacrylamides,vinyl acetate, and vinyl butyrate and vinyl benzoate and mixturesthereof. The amount of these other vinyl group monomers can be used atless than 50 weight percent based on the acrylates.

Additional monomers used in the polymerization can includedi(meth)acrylates and trimethacrylates.

The encapsulation monomers may contain mixtures of acrylates, acrylics,and vinyl monomers as described above.

Encapsulation Process

The encapsulation process occurs when the monomers are polymerized inthe presence of the pigment which has been dispersed with polymericdispersant. The encapsulated pigment has improved stability relative toa polymerically dispersed pigment that has not been encapsulated. Whenthe encapsulated pigment is used in an inkjet ink the inks have betterstorage stability, improved performance in inkjet inks with aggressivesolvent in the formulation, and the optical properties are comparable tothe dispersed pigments that are not encapsulated. The durability of theprints from these encapsulated pigmented inks is excellent. Theseencapsulated pigments have utility in all inkjet printheads, includingpiezo and thermal printheads.

Prior to the encapsulation process, the monomers are mixed into anaqueous mixture which contains the polymerically dispersed pigment. Themonomers may have a compatibility with the polymerically dispersedpigment such that they are associated with the polymerically dispersedpigment prior to the polymerization. The mixing methods can include highsheer mixing.

This aqueous mixture of the polymerically dispersed pigments, andmonomer(s) is mixed using high shear mixing. Examples of equipment forthe high shear mixing includes a ultrasonicator, media mill, ahorizontal mini mill, an attritor, or by passing the mixture through aplurality of nozzles within a liquid jet interaction chamber at a liquidpressure of at least 5,000 psi.

Following this high shear mixing that produces a mixture of thedispersed pigment, and the monomers, the polymerization of the monomersis initiated by addition of appropriate initiators which includeperoxides, azo compounds and redox initiators. The temperature of thepolymerization is determined by the temperature required for theinitiator and the properties of the monomers.

While not wishing to be bound by theory, the monomers apparently have anaffinity for the polymerically dispersed pigment such that the monomerscan be polymerized. These polymerized monomers in conjunction with thedispersed pigment produce the encapsulated pigment. The properties ofthe encapsulated pigment may lead to the conclusion that the polymerfrom the added monomer must be in solid mixture which surrounds thepigment. For instance, polymerically dispersed pigments can have thepolymeric dispersant displaced by a strong solvent such as butylcellosolve. When the encapsulated pigment is challenged with a strongsolvent it is stable relative to the polymerically dispersed pigmentwhich has not been encapsulated. It is expected that the polymer derivedfrom the monomers added is an independent polymer in the solid mixturethat surrounds the pigment. Furthermore, the added encapsulated monomersare not chemically reacted with either the dispersant polymer or thepolyurethane solids of the polyurethane dispersion. The dispersantpolymer, by design, has no reactive sites with which the acrylatemonomers can copolymerize. Disubstituted monomers can be used with theacrylate monomers to produce polymers with some branching.

Another way to observe the encapsulated pigment is to study the densityof the encapsulated pigment before and after the encapsulation. One wayto determine the density is to test the encapsulated pigment in aglycerol, sucrose or similar chemical gradient. Glycerol and water areadded into a centrifuge tube and the encapsulated pigment is added.After centrifugation the encapsulated pigment will be at a level whichreflects its density. The encapsulated pigment has lower density thanthe polymerically dispersed pigment. In the density gradientcentrifugation method the free polymer will be in the supernatant andthe encapsulated pigment will be in the bottom of the centrifuge tube.

The product of this process is a stable, dispersed pigment. This stablepigment dispersion is one that has less than 10% particle size growthand no flocculation when the dispersion is stored at room temperaturefor at least a week. More rigorous testing that entail acceleratedtesting by heating samples for a week or more can also be used todetermine the stability of the particle dispersions. The optimalparticle dispersion stability would depend on the particlecharacteristics and/or final use. Another criterion for a stabledispersed particle is that it can be processed under the dispersingprocess conditions, not gel or have other adverse properties.

The encapsulated pigments of this invention demonstrate improved storagestability, improved stability when tested in a solvent challengeprocedure. The inks derived from these encapsulated pigments performbetter in extended jettability tests. The printed inks are more durablethan those inks which contain pigments that are not encapsulated.

Amounts/Ratios of the Ingredients

For inkjet inks the mass ratio of pigment to polymeric dispersant rangesfrom 0.33 to 400. This ratio is based on the mass of the pigment andthat of the polymeric dispersant added to the dispersion. For organicpigments the ratio is 0.33 to 12, optionally 0.5 to 10. For inorganicpigments the ratio is 3 to 400, optionally 5 to 200.

The ratio of encapsulation monomer to pigment for the encapsulating stepis 0.1 to 10 based on the pigment and measured on a weight/weight basis.Thus, if there are 100 grams of pigment in a liter of aqueousdispersion, 10 to 1000 grams are added to the polymeric dispersion ofthe pigment prior to encapsulation. Optionally, the ratio ofencapsulation monomer to pigment is 0.15 to 5 or alternatively 0.25 to1.

There is a balance of properties between the polymeric dispersant usedand the monomers used such that properties of the polymeric dispersantand pigment/dispersant [P/D] ratio may limit how much encapsulationmonomer may be used. For instance, for the more hydrophobicencapsulation monomers the P/D may need to be higher.

In the case of organic pigments, the inkjet ink may contain up toapproximately 30% of the encapsulated pigment, optionally 0.11 to 25%,and further from 0.25 to 15% pigment by weight based on the total inkweight of the ink. If an inorganic pigment is selected, the ink willtend to contain higher weight percentages of pigment than withcomparable inks employing organic pigment, and the ink may be as high as75% in some cases, since inorganic pigments generally have higherspecific gravities than organic pigments. Examples of inorganic pigmentsinclude titanium dioxide, iron oxides, and the like.

Inkjet Ink Components

Aqueous Carrier Medium

The aqueous carrier medium (aqueous vehicle) for the inkjet inks whichutilize the encapsulated pigment described above is water or a mixtureof water and at least one water-miscible organic solvent. Selection of asuitable mixture depends on requirements of the specific application,such as desired surface tension and viscosity, the selected pigment,drying time of the pigmented inkjet ink, and the type of paper ontowhich the ink will be printed. Representative examples of water-solubleorganic solvents that may be selected include (1) alcohols, such asmethyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol,n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol,furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones orketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol;(3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such asethyl acetate, ethyl lactate, ethylene carbonate and propylenecarbonate; (5) polyhydric alcohols, such as ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, tetraethylene glycol,polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol1,2,6-hexanetriol and thiodiglycol; (6) lower alkyl mono- or di-ethersderived from alkylene glycols, such as ethylene glycol mono-methyl (or-ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether,propylene glycol mono-methyl (or -ethyl)ether, triethylene glycolmono-methyl (or -ethyl) ether and diethylene glycol di-methyl (or-ethyl) ether; (7) nitrogen containing cyclic compounds, such aspyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone;and (8) sulfur-containing compounds such as dimethyl sulfoxide andtetramethylene sulfone.

A mixture of water and a polyhydric alcohol, such as diethylene glycol,is preferred as the aqueous carrier medium. In the case of a mixture ofwater and diethylene glycol, the aqueous carrier medium usually containsfrom 30% water/70% diethylene glycol to 95% water/5% diethylene glycol.The preferred ratios are approximately 60% water/40% diethylene glycolto 95% water/5% diethylene glycol. Percentages are based on the totalweight of the aqueous carrier medium. A mixture of water and butylcarbitol is also an effective aqueous carrier medium.

The amount of aqueous carrier medium in the ink is typically in therange of 70% to 99.8%, and preferably 80% to 99.8%, based on totalweight of the ink.

The aqueous carrier medium can be made to be fast penetrating (rapiddrying) by including surfactants or penetrating agents such as glycolethers and 1,2-alkanediols. Glycol ethers include ethylene glycolmonobutyl ether, diethylene glycol mono-n-propyl ether, ethylene glycolmono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethyleneglycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether,diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butylether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol,propylene glycol mono-t-butyl ether, propylene glycol mono-n-propylether, propylene glycol mono-iso-propyl ether, propylene glycolmono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropyleneglycol mono-n-propyl ether, and dipropylene glycol mono-isopropyl ether.1,2-Alkanediols are preferably 1,2-C4-6 alkanediols, most preferably1,2-hexanediol. Suitable surfactants include ethoxylated acetylene diols(e.g. Surfynols® series from Air Products), ethoxylated primary (e.g.Neodol® series from Shell) and secondary (e.g. Tergitol® series fromUnion Carbide) alcohols, sulfosuccinates (e.g. Aerosol® series fromCytec), organosilicones (e.g. Silwet® series from Witco) and fluorosurfactants (e.g. Zonyl® series from DuPont).

The amount of glycol ether(s) and 1,2-alkanediol(s) added must beproperly determined, but is typically in the range of from 1 to 15% byweight and more typically 2 to 10% by weight, based on the total weightof the ink. Surfactants may be used, typically in the amount of 0.01 to5% and preferably 0.2 to 4%, based on the total weight of the ink.

Other Additives

Other additives, such as biocides, humectants, chelating agents andviscosity modifiers, may be added to the ink for conventional purposes.Biocides may be used to inhibit growth of microorganisms. Inclusion ofsequestering (or chelating) agents such as ethylenediaminetetraaceticacid (EDTA), iminodiacetic acid (IDA),ethylenediamine-di(o-hydroxyphenylacetic acid) (EDDHA), nitrilotriaceticacid (NTA), dihydroxyethylglycine (DHEG),trans-1,2-cyclohexanediaminetetraacetic acid (CyDTA),diethylenetriamine-N,N,N′,N″, N″-pentaacetic acid (DTPA), andglycoletherdiamine-N,N,N′,N′-tetraacetic acid (GEDTA), and saltsthereof, may be advantageous, for example, to eliminate deleteriouseffects of heavy metal impurities.

Other polymer additives to the ink, if used, can be soluble or dispersedpolymer(s). They can be any suitable polymer, for example, solublepolymers may include linear homopolymers, copolymers, block polymers ornatural polymers. They also can be structured polymers including graftor branched polymers, stars, dendrimers, etc. The dispersed polymers caninclude latexes, polyurethane dispersions, etc. The polymers may be madeby any known process including but not limited to free radical, grouptransfer, ionic, RAFT, condensation and other types of polymerization.Useful classes of polymers include, for example, acrylics,styrene-acrylics, urethanes and alginates. These polymer additives areadded at the time an ink is made, after any encapsulation is complete.

These polymer additives can be effective in improving gloss and otherproperties while not sacrificing optical density. Other properties thatcan be affected by the polymer additives include, for example,reliability for thermal inkjet printing and image durability.

Ink Properties

Drop velocity, separation length of the droplets, drop size and streamstability are greatly affected by the surface tension and the viscosityof the ink. Inkjet inks typically have a surface tension in the range of20 dyne/cm to 70 dyne/cm at 25° C. Viscosity can be as high as 30 cP at25° C., but is typically somewhat lower. The ink has physical propertiesthat can be adjusted to the ejecting conditions and printhead design.The inks should have excellent storage stability for long periods so asnot clog to a significant extent in an inkjet apparatus. Further, theink should not corrode parts of the ink-jet printing device it comes incontact with, and it should be essentially odorless and non-toxic.

Although not restricted to any particular viscosity range or printhead,lower viscosity inks can be used, and may be preferred for certainapplications. Thus the viscosity (at 25° C.) of the inks can be lessthan 7 cP, less than 5 cP, or even less than 3.5 cP.

The inkjet inks described herein may be jetted from any of the inkjetprintheads, including drop-on-demand, piezo and thermal printheads. Theprinted substrates can include all types of paper, textiles, andhydrophobic surfaces.

Ink Sets

Ink sets suitable for use with the present disclosure comprise at leastthree primary color inks: a cyan ink, a magenta ink and a yellow ink(CMY). The ink set may optionally contain additional inks, andparticularly a black ink (making a CMYK ink set). At least one of colorsmust have the pigment encapsulated by the process described above.

When the ink set contains a black ink, pigment is generally preferredfor black from the standpoint of high optical density. A black pigmentcan be a carbon black pigment, and optionally a self-dispersed pigmentblack may be used. However, when the black is prepared by the presentlydisclosed process the black ink will be black pigment with a polymericdispersant and, in turn, encapsulated by polymerizing monomers.

The ink set may further comprise a fixing solution. See, for example,U.S. Pat. Nos. 5,746,818, 6,450,632, US Patent Application PublicationNo. 20020044185, EP Patent Specification No. 1258510 and US PatentApplication Publication No. 20040201658.

Examples

The following examples illustrate the various embodiments of the presentdisclosure without, however, being limited thereto. Tests listed hereare those that are commonly used for testing pigment dispersions andinkjet inks.

The particle size for the pigment dispersions and the inks weredetermined by dynamic light scattering using a MICROTRAC UPA 150analyzer from Honeywell/Microtrac (Montgomeryville Pa.).

This technique is based on the relationship between the velocitydistribution of the particles and the particle size. Laser generatedlight is scattered from each particle and is Doppler shifted by theparticle Brownian motion. The frequency difference between the shiftedlight and the unshifted light is amplified, digitalized and analyzed torecover the particle size distribution. Results are reported as D50 andD95 and particles less than 204 nm.

MW characterization of the Polymeric Dispersants

Molecular weights of the polymers were determined by GPC using poly(methyl methacrylate) standards with tetrahydrofuran as the eluent. Themolecular weight is routinely reported as number average molecularweight, Mn or optionally the weight average molecular weight Mw. Thepolymeric dispersants are not limited to Gaussian distribution ofmolecular weight, but may have other distributions such as bimodaldistributions.

Free polymer dispersant, that which is unbound to the pigment in an inkor pigment dispersion, is determined from the gravimetric % solids ofthe supernatant of the sample, after the pigment is removed bycentrifugation.

Centrifugation Method:

-   -   1. The pigment dispersion sample is diluted with deionized water        to 5% pigment.    -   2. The diluted sample is centrifuged at 20,000 rpm for 2 hours.    -   3. The pigment-free supernatant is analyzed for % solids content        (assumed to be free polymeric dispersant).    -   4. The amount of free polymeric dispersant in the sample is        determined gravimetrically by drying the supernatant obtained        from the centrifugation step weighing the solids left behind        after weighing.    -   5. The bound polymeric dispersant is the difference between the        total polymeric dispersant and the free polymeric dispersant.

Free polymer in the final encapsulated pigment dispersion, that which isunbound to the pigment in an ink or pigment dispersion, is determined bythe density gradient centrifugation method:

-   -   1. Make up glycerol solution (75/25 solution) three parts        glycerol to one part water by weight.    -   2. Add 75/25 glycerol water solution to each centrifuge tube        (approx. ⅓ of tube volume, ˜11-12 g)    -   3. Slowly add 10.0 grams of the 5% pigment dispersion to be        tested. Add by letting the dispersion slowly drain down the side        of the tube to layer on top of the glycerol solution.    -   4. Centrifuge two hours at 25 degrees C. and 50,000 RPM    -   5. Carefully withdraw top layer containing polymer using the        high intensity light to find polymer and a long glass pipette        and place into a tared aluminum weigh dish.    -   6. Bake for 3 to 4 hours in 95 deg C. convection oven to remove        water and then transfer to a 150 deg C. vac. oven until dry        (overnight).    -   7. Calculate amount of free polymer in the supernatant.    -   8. The bound polymer is the difference between the total polymer        and the free polymer.

The inks were tested by printing on various substrates with HP printers.Plain paper, glossy paper and brochure paper were tested. Thejettability of the inks over a long print cycle was done by printingfrom an HP45 printhead. The amount of ink from each drop was measuredperiodically and the test design was to eject up to 50 mLs of ink foreach ink. The quality of this jettability was judged by the total numberof mLs of ink jetted, the stability of the amount jetted and thevariability of the amount jetted.

The optical density was measured using a Greytag-Macbeth SpectroEye™instrument (Greytag-Macbeth AG, Regensdorf, Switzerland).

The durability of the image towards highlighter smear was done using aFaber-Castel highlighter pen after the printed image was allowed to dryfor one hour after printing. The image was marked twice, the first markwas with a single pass with the highlighter and the second mark was withtwo passes with the highlighter. These highlighter marks were tested bymeasuring the optical density in the region on the smear adjacent to theprinted image. The optical density is corrected for a highlighter thatis not drawn across the printed image. That is, after the highlighter isdrawn across the printed marks the OD is measured in the yellowhighlighted area adjacent to the printed marks. In this area will be thehighlighter and the transferred pigment. The amount of optical densitymeasured is an indication of how much of the printed image is smearedand a higher number demonstrates a worse result. This smear is reportedin milliOD units.

Dispersant Polymer 1 Polyurethane 1 (DEA Terminated TMXDI/UH-50/DMPA)

To a dry, alkali- and acid-free, 2 liter flask equipped with anadditional funnel, a condenser and a stirrer, under a nitrogenatmosphere was added Eternacoll® UH-50 (117.0 g), dimethylol propionicacid (87.0 g) and Sulfolane (220.0 g). The contents were heated to 115°C. and mixed under a nitrogen gas purge for 30 minutes. The temperaturewas then lowered to 60° C. and DBTDL (0.08 g) was added followed byTMXDI (238.0 g) via the addition funnel. The residual TMXDI in theadditional funnel was rinsed into the flask with Sulfolane (15.0 g). Thestirred reaction mass was allowed to exotherm. When exotherm began toslow, the temperature was maintained at 100° C. while monitoring theisocyanate content until it reached 1.06%. The temperature was loweredto 60° C. To the flask was added DEA (18.04 g) via the additional funnelfollowed by rinsing the residual BMEA in additional funnel into theflask with Sulfolane (5.0 g). The mixture was maintained at 60° C. for90 minutes. A solution of 45% KOH in water (56.56 g) and additionalde-ionized water (776.87 g) were added over a period of 5 minutes togive a 70% neutralized polyurethane resin in water. This was allowed tostir and cool to room temperature to provide a polyurethane dispersionwith 27.49% of solids and a measured acid number of 79.03 mg KOH/grampolymer.

Dispersant Polymer 2 (Structured Polymer, Triblock) ETEGMA//BZMA//MAA3.6//13.5//10.8

A 3-liter flask was equipped with a mechanical stirrer, thermometer, N₂inlet, drying tube outlet, and addition funnels. Tetrahydrofuran THF,291.3 gm, was charged to the flask. The catalyst tetrabutyl ammoniumm-chlorobenzoate, 0.44 ml of a 1.0 M solution in acetonitrile, was thenadded to the flask. Initiator, 1,1-bis(trimethylsiloxy)-2-methylpropene, 20.46 gm (0.0882 moles) was injected into the flask. Feed I[tetrabutyl ammonium m-chlorobenzoate, 0.33 ml of a 1.0 M solution inacetonitrile and THF, 16.92 gm] was started and added over 185 minutes.Feed II [trimethylsilyl methacrylate, 152.00 gm (0.962 moles)] wasstarted at 0.0 minutes and added to the flask over 45 minutes. Onehundred and eighty minutes after Feed II was completed (over 99% of themonomers had reacted) Feed III [benzyl methacrylate, 211.63 gm (1.20moles) was started and added over 30 minutes. Forty minutes after FeedIII was completed (over 99% of the monomers had reacted) Feed IVmethacrylate, 78.9 gm (0.321 moles) was started and added over 30minutes.

At 400 minutes, 73.0 gm of methanol and 111.0 gm of 2-pyrrolidone wasadded to the above solution and distillation began. During the firststage of distillation, 352.0 gm of material was removed. Then more2-pyrrolidone 340.3 gm was added and an additional 81.0 gm of materialwas distilled out. Finally, 2-pyrrolidone, 86.9 gm total, was added.

The polymer has a composition of ETEGMA//BZMA//MAA 3.6//13.5//10.8. Ithas a molecular weight of Mn=4,200, acid value 162.

Pigment Dispersions

The pigmented dispersions were prepared using a two-step processinvolving a first mixing step followed by a second grinding step. Thefirst step comprises mixing of all the ingredients, that is, pigment,dispersants, liquid carriers, neutralizing agent, and any optionaladditives to provide a blended “premix”. Typically all liquidingredients were added first, followed by the neutralizing agent, thenthe dispersants, and lastly the pigment. Mixing was done in a stirredmixing vessel, and a high-speed disperser (HSD) was used for the mixingstep. A Cowels type blade was attached to the HSD and was operated atfrom 500 rpm to 4000 rpm, which provided optimal shear to achieve thedesired mixing. Adequate mixing was usually achieved after mixing underthe conditions described above for a period of from 15 to 120 minutes toobtain the premix mixture.

The second step was grinding of the premix to produce a pigmenteddispersion. A lab-scale Eiger Minimill (Model M250, VSE EXP)manufactured by Eiger Machinery Inc., Chicago, Ill. was employed.Grinding was accomplished by charging 820 grams of 0.5 YTZ® zirconiamedia to the mill. The mill disk was operated at a speed between 2000rpm and 4000 rpm, and typically between 3000 rpm and 3500 rpm. Thedispersion was processed using a re-circulation grinding process with atypical flow rate through the mill at between 200 to 500 grams/minute,and more typically at 300 grams/minute. The milling may be done using astaged procedure in which a fraction of the solvent is held out of thegrind and added after milling is completed. This is done to achieveoptimal rheology that maximizes grinding efficiency. The amount ofsolvent held out during milling varies by dispersion, and is typicallybetween 200 to 400 grams for a batch size with a total of 800 grams.Typically, the dispersions of the present invention were subjected to atotal of 4 hours of milling.

For black dispersions, an alternate milling process using aMicrofluidizer was used. Microfluidization is a non-media millingprocess in which milling is done by pigment impingement through nozzlesunder high pressures. Typically, pigment dispersions were processed at15,000 psi with a flow rate of 400 grams/minute for a total of 12 passesthrough the mill. In making the black dispersions in the Examples, alab-scale (Model M-110Y, available from Microfluidics of Newton, Mass.)high pressure pneumatic Microfluidizer with a diamond Z Chamber wasemployed.

Alternatively, the pigment dispersion for step (a) was prepared using asolvent milling process, in which 6 parts of an un-neutralizeddispersant were combined with 16 parts of a pigment in 50 parts of waterand 27.5 parts of a solvent (methyl ethyl ketone), and sufficient KOH toneutralize the dispersant to a degree of 90%. This premix was dispersedin a High Speed Disperser (HSD) at 2000 rpm for 2 hours. The resultingpremix was sufficiently milled to achieve an acceptable particle size.The milled dispersion was then distilled at 67° C. under vacuum toremove the solvent.

Preparation of Pigmented Dispersion K1

The following procedure was used to prepare a black pigmented dispersionusing Nipex 180 and Dispersant 1. Using an microfluidizer, a premix wasprepared at typically 20-30% pigment loading and the targeted dispersantlevel was selected at a pigment/dispersant (P/D) ratio of 2.0. A P/D of2.0 corresponds to a 40% dispersant level on pigment. A co-dispersant,Surfynol 104 in Dowanol DPM at a P/D=100 was added to the totaldispersion formulation to facilitate wetting of pigment and dissolutionof dispersant in the premix stage for ease of grinding during millingstage. Dispersant 1 was pre-neutralized with KOH to facilitatesolubility and dissolution into water. An additional 6.91 g of a 45% KOHsolution in water was added. During the premix stage and milling stage,de-ionized water (1200 g) was added to adjust viscosity and controltemperature. After completion of the milling stage, the remainingletdown of de-ionized water (450.0 g) was added and thoroughly mixed.The final pigment dispersion contains 23.15% of solids.

The pigment dispersion was purified using an ultrafiltration process toremove co-solvent(s) and excess dispersant, and filter out otherimpurities that may be present. After completion, the pigment level inthe dispersion was reduced to 10 to 15%. A single black dispersion wasprepared using the Polyurethane Dispersant 1.

Polyurethane Pigmented Pigment/ Dispersant Particle Size DispersionPigment Dispersant No. D50 (nm) D95 (nm) K1 Nipex 180 2 1 107 185Preparation of Cross-linked Pigment Dispersion XL-K1

In the cross-linking step, Denacol® 321 was mixed with one of thepigmented Dispersion K1, and heated at temperatures between 60° C. and80° C. with efficient stirring for 6-8 hours. After the cross-linkingreaction was completed, the pH was adjusted to at least about 8.0 ifneeded. The composition of the cross-linked Pigment Dispersion XL-K1 issummarized below.

Cross-linked Pigmented Cross-linkable Cross-linking DispersionDispersion Moiety Compound XL-K1 K1 COOH, OH Denacol ® 321

EXAMPLES Encapsulation Example 1

Nipex 180 (black) dispersion was prepared with Pigment Dispersion K1described above so that pigment to dispersant ratio was 4.1.Encapsulation Monomer mixture was prepared by mixing 6.2 gram ETEGMA,0.69 gram BZMA, and 0.10 gram of Ethoxylated bisphenol A dimethacrylate.29.98 gram of water was added in 172.32 gram of the black dispersion,and the encapsulation monomer mixture was added to the mixture andmagnetic stirred for 10 min. This mixture of pigment dispersion andencapsulation monomer mixture was also sonicated for 30 min (2 sec on, 4sec off) in ice bath with 30% of full power. The particle size dataafter sonication are D50 102 nm and D95 175 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.76gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 163 nm and D95 448 nm.

Encapsulation Example 2

Nipex 180 (black) dispersion was prepared with Pigment Dispersion K1described above so that pigment to dispersant ratio was 4.1.Encapsulation Monomer mixture was prepared by mixing 4.69 gram ETEGMA,0.52 gram BZMA, and 0.08 gram of Ethoxylated bisphenol A dimethacrylate.30.22 gram of water was added in 173.7 gram of the black dispersion, andthe encapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 102 nm and D95 175 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.83gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 108 nm and D95 176 nm.

Encapsulation Example 3

Nipex 180 (black) dispersion was prepared by MEK milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 3.6.Encapsulation Monomer mixture was prepared by mixing 5.5 gram ETEGMA,0.62 gram BZMA, and 0.10 gram of Ethoxylated bisphenol A dimethacrylate.73.42 gram of water was added in 120.1 gram of the black dispersion, andthe encapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 101 nm and D95 170 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.81gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 125 nm and D95 219 nm.

Encapsulation Example 4

Nipex 180 (black) dispersion was prepared by MEK milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 3.6.Encapsulation Monomer mixture was prepared by mixing 4.18 gram ETEGMA,0.46 gram BZMA, and 0.07 gram of Ethoxylated bisphenol A dimethacrylate.73.94 gram of water was added in 121 gram of the black dispersion, andthe encapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 98 nm and D95 151 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.49gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 99 nm and D95 177 nm.

Encapsulation Example 5

Nipex 180 (black) dispersion was prepared with Pigment Dispersion K1described above so that pigment to dispersant ratio was 3.8.Encapsulation Monomer mixture was prepared by mixing 5.93 gram ETEGMA,0.66 gram BZMA, and 0.10 gram of Ethoxylated bisphenol A dimethacrylate.39.54 gram of water was added in 163 gram of the black dispersion, andthe encapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 98 nm and D95 160 nm. The sonicated mixture was transferred to250 ml reactor equipped with an agitator and a condenser. The reactorwas then heated to 82° C. 10.22 gram of 2.5% water soluble initiator,Vazo® 68 was then charged for an hour and polymerized at 82° C. foradditional two hours. The particle size data after polymerization areD50 109 nm and D95 188 nm.

Encapsulation Example 6

Nipex 180 (black) dispersion was prepared with Pigment Dispersion K1described above) so that pigment to dispersant ratio was 3.8.Encapsulation Monomer mixture was prepared by mixing 4.48 gram ETEGMA,0.50 gram BZMA, and 0.07 gram of Ethoxylated bisphenol A dimethacrylate.39.86 gram of water was added in 164.24 gram of the black dispersion,and the encapsulation monomer mixture was added to the mixture andmagnetic stirred for 10 min. This mixture of pigment dispersion andencapsulation monomer mixture was also sonicated for 30 min (2 sec on, 4sec off) in ice bath with 30% of full power. The particle size dataafter sonication are D50 100 nm and D95 171 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.14gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 103 nm and D95 165 nm.

Encapsulation Example 7

Nipex 180 (black) dispersion was prepared by two step milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 followed by UF process so that pigment to dispersantratio was 3.1. Encapsulation Monomer mixture was prepared by mixing 6.26gram ETEGMA, 0.7 gram BZMA, and 0.10 gram of Ethoxylated bisphenol Adimethacrylate. 20.87 gram of water was added in 181.47 gram of theblack dispersion, and the encapsulation monomer mixture was added to themixture and magnetic stirred for 10 min. This mixture of pigmentdispersion and encapsulation monomer mixture was also sonicated for 30min (2 sec on, 4 sec off) in ice bath with 30% of full power. Theparticle size data after sonication are D50 108 nm and D95 189 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.02gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 125 nm and D95 241 nm.

Encapsulation Example 8

Nipex 180 (black) dispersion was prepared by the two step milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 followed by UF process so that pigment to dispersantratio was 3.1. Encapsulation Monomer mixture was prepared by mixing 4.73gram ETEGMA, 0.53 gram BZMA, and 0.08 gram of Ethoxylated bisphenol Adimethacrylate. 21.04 gram of water was added in 182.94 gram of theblack dispersion, and the encapsulation monomer mixture was added to themixture and magnetic stirred for 10 min. This mixture of pigmentdispersion and encapsulation monomer mixture was also sonicated for 30min (2 sec on, 4 sec off) in ice bath with 30% of full power. Theparticle size data after sonication are D50 97 nm and D95 175 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.34gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 98 nm and D95 165 nm.

Encapsulation Example 9

Nipex 180 (black) dispersion was prepared by the two step milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 followed by UF process so that pigment to dispersantratio was 2.6. Encapsulation Monomer mixture was prepared by mixing 4.62gram ETEGMA, 0.51 gram BZMA, and 0.08 gram of Ethoxylated bisphenol Adimethacrylate. 35.91 gram of water was added in 168.22 gram of theblack dispersion, and the encapsulation monomer mixture was added to themixture and magnetic stirred for 10 min. This mixture of pigmentdispersion and encapsulation monomer mixture was also sonicated for 30min (2 sec on, 4 sec off) in ice bath with 30% of full power. Theparticle size data after sonication are D50 111 nm and D95 167 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.21gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 108 nm and D95 178 nm.

Encapsulation Example 10

E-02 (Magenta) dispersion was prepared by MEK milling method describedabove using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 4.0.Encapsulation Monomer mixture was prepared by mixing 3.86 gram2-(2-Ethoxyethoxy) Ethyl Acrylate, 1.65 gram Hexyl Methacrylate, and0.08 gram of Ethoxylated bisphenol A dimethacrylate. The monomer mixturewas added in 184.87 gram of the magenta dispersion by 10 min magneticstir. This mixture of pigment dispersion and encapsulation monomermixture was also sonicated for 30 min (2 sec on, 4 sec off) in ice bathwith 30% of full power. The particle size data after sonication are D5089 nm and D95 173 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.45gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 104 nm and D95 203 nm.

Encapsulation Example 11

Nipex 180 (black) dispersion was prepared by process described above inExample 1 using IPDI/T650/DMPA/BMEA so that pigment to dispersant ratiowas 4.1. Encapsulation Monomer mixture was prepared by mixing 10.15 gramETEGMA, 1.13 gram BZMA, 0.47 gram Stearyl MA and 0.17 gram ofEthoxylated bisphenol A dimethacrylate and the encapsulation monomermixture was added in 159.65 gram of the black dispersion, and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power.

The microfluidized mixture was transferred to 250 ml reactor equippedwith an agitator and a condenser. The reactor was then heated to 82° C.8.42 gram of 2.5% water soluble initiator, Vazo® 68 was then charged foran hour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 171 nm and D95 310 nm.

Encapsulation Example 12

Nipex 180 (black) dispersion was prepared by the two step milling methoddescribed above using KOH neutralized acrylic dispersant polymer 1ETEGMA//BzMA//MAA 3.6//13.6//10.8 followed by UF process so that pigmentto dispersant ratio was 2.82. The pigment dispersion was crosslinked byadding Denacol® 321. The Denacol was 0.40 equivalent weight based on theacid number of the dispersant as described. After crosslinking of thepolymeric dispersant the dispersion was purified by ultrafiltration.

Encapsulation Monomer mixture was prepared by mixing 3.25 gram2-(2-Ethoxyethoxy) Ethyl Acrylate, 1.39 gram Hexyl MA, and 0.07 gram ofEthoxylated bisphenol A dimethacrylate. The encapsulation monomermixture was added to the black dispersion and magnetic stirred for 10min. This mixture of pigment dispersion and encapsulation monomermixture was also sonicated for 30 min (2 sec on, 4 sec off) in ice bathwith 30% of full power. The particle size data after sonication are D50107 nm and D95 165 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 6.34gram of 2.5% water soluble initiator Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 102 nm and D95 170 nm.

Comparable Encapsulation Example 1

Nipex 180 (black) dispersion was prepared by two step milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 3.7.Encapsulation Monomer mixture was prepared by mixing 3.54 gram ETEGMA,0.89 gram BZMA, and 0.18 gram of Ethyleneglycol dimethacrylate. 22.88gram water dispersible preformed PU (19.31% solid, Preformed PU 2 inIJ302) was mixed with 53 gram of water and mixed with the monomermixture by 10 min magnetic stir and also 6 min sonication (2 sec on, 4sec off) in ice bath with 30% of full power. The mixture was added in119.36 gram of the black dispersion and magnetic stirred for 10 min.This mixture of pigment dispersion and encapsulation monomer mixture wasalso sonicated for 30 min (2 sec on, 4 sec off) in ice bath with 30% offull power. The particle size data after sonication are D50 101 nm andD95 163 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.86gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 99 nm and D95 168 nm.

Comparable Encapsulation Example 2

Nipex 180 (black) dispersion was prepared by two step milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 2.3.Encapsulation Monomer mixture was prepared by mixing 9.26 gram ETEGMA,1.05 gram BZMA, and 0.16 gram of Ethoxylated bisphenol A dimethacrylate.61.7 gram of water was added in 137.6 gram of the black dispersion, andthe encapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 101 nm and D95 159 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 9.67gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 93 nm and D95 169 nm.

Comparable Encapsulation Example 3

Nipex 180 (black) dispersion was prepared by MEK milling methoddescribed above using acrylic dispersant polymer 1 ETEGMA//BzMA//MAA3.6//13.6//10.8 so that pigment to dispersant ratio was 2.0. Most offree dispersant remained in the MEK milled dispersion was removed bycentrifuging in water followed by discarding supernatant solution.Centrifuged pigment dispersion was redispersed in water by sonicationand resulting pigment to dispersant ratio was 2.83. EncapsulationMonomer mixture was prepared by mixing 6.91 gram ETEGMA, 0.56 gram HexylMA, and 0.11 gram of Ethoxylated bisphenol A dimethacrylate. 56.06 gramof water was added in 107.94 gram of the black dispersion, and theencapsulation monomer mixture was added to the mixture and magneticstirred for 10 min. This mixture of pigment dispersion and encapsulationmonomer mixture was also sonicated for 30 min (2 sec on, 4 sec off) inice bath with 30% of full power. The particle size data after sonicationare D50 106 nm and D95 185 nm.

The sonicated mixture was transferred to 250 ml reactor equipped with anagitator and a condenser. The reactor was then heated to 82° C. 6.03gram of 2.5% water soluble initiator, Vazo® 68 was then charged for anhour and polymerized at 82° C. for additional two hours. The particlesize data after polymerization are D50 106 nm and D95 189 nm.

For examples 1-11 and Comparative Examples 1-3 properties are listed inTable 1 and 2. For the dispersed pigment the free polymer dispersant isshown in table 1 as FP/P and was measured by the centrifugation method.For Example 3 FP/P analysis was done by both the centrifugation methodand Glycerol density column method showed the same values for the basedispersion used in Exp. 3. (centrifugation method: FP/P 3.18, BP/P21.82; density gradient centrifugation method: FP/P 2.7, BP/P 22.3)

TABLE 1 Dispersed Pigment and Monomers Step (a) Dispersed Mass ratiosfor Pigment polymerization FPD/P BP/P P/D P:D:M Exp 1 0.02 0.23 4.00200:49:67.7 Exp 2 0.02 0.23 4.00 200:49:50.8 Exp 3 0.03 0.22 4.00200:55.5:67.7 Exp 4 0.03 0.22 4.00 200:55.5:50.8 Exp 5 0.05 0.21 3.85200:52.4:67.7 Exp 6 0.05 0.21 3.85 200:52.4:50.8 Exp 7 0.08 0.24 3.13200:64.6:67.7 Exp 8 0.08 0.24 3.13 200:64.6:50.8 Exp 9 0.1 0.30 2.50200:76.1:50.8 Exp 10 0.08 0.17 4.00 200:50:50.8 Exp 11 0.05 0.19 4.1200:48.8:147.7 Exp 12 0.06 0.30 2.73 200:73.2:50.8 Comp 1 0.15 0.1 4.00200:54.1:52 Comp 2 0.26 0.15 2.44 200:88:101.5 Comp 3 <0.05 0.35 2.83200:70.7:81.2 FPD/P free polymer dispersant as a wt fraction of pigmentBP/P bound polymer as wt fraction of pigment P/D Pigment/dispersantMonomercomposition:

-   Examples 1-9 and Comparative 2; 90:10:1.5 weight ratio of ethyl    triethyleneglycol methacrylate:benzyl methacrylate:ethoxylated    bisphenol A dinnethacrylate-   Example 10 and 12: 70:30:1.5 2-(2-Ethoxyethoxy) Ethyl Acrylate:    hexyl methacrylate: ethoxylated bisphenol A dinnethacrylate-   Example 11; 90:10:4:1.5 weight ratio of ethyl triethyleneglycol    methacrylate:benzyl methacrylate:Stearyl methacrylate:ethoxylated    bisphenol A dimethacrylate.-   Comparative Example 1: 40:10:2 weight ratio of ethyl    triethyleneglycol methacrylate:benzyl methacrylate:ethoxylated    bisphenol A dimethacrylate-   Comparative Example 3: 91:7.4:1.5 weight ratio of ethyl    triethyleneglycol methacrylate:hexyl methacrylate:ethoxylated    bisphenol A dimethacrylate

For the final encapsulated pigments the free polymer is shown in thecolumn labeled FP/P and the free polymer to bound polymer in columnlabeled FP/BP in Table 2.

TABLE 2 Encapsulated Pigment P/P′ FP/P BP/P FP/BP Exp 1 1.7 0.03 0.550.05 Exp 2 2 0.11 0.39 0.28 Exp 3 1.6 0.07 0.54 0.13 Exp 4 1.9 0.09 0.440.2 Exp 5 1.7 0.11 0.49 0.22 Exp 6 1.9 0.21 0.3 0.7 Exp 7 1.5 0.23 0.430.53 Exp 8 1.9 0.14 0.4 0.35 Exp 9 1.6 0.29 0.34 0.85 Exp 10 2 0.05 0.450.11 Exp 11 1.1 0.12 0.8 0.15 Exp 12 1.6 0.21 0.41 0.51 Comp 1 1.4 0.420.3 1.4 Comp 2 1.1 0.38 0.39 0.97 Comp 3 1.32 0.42 0.33 1.27 P/P′Pigment/total polymer as a ratio FP/P free polymer as wt fraction ofpigment BP/P bound polymer as wt fraction of pigment FP/BP Freepolymer/Bound Polymer as wt/wt

For selected examples the D50 and D95 were measured before and afterpolymerization and those results are listed in Table 3.

The same selected examples were formulated into inkjet formulations andtested by ageing the inks at 70° C. for 7 days and retesting theparticle size.

TABLE 3 Particle Size: Before/After Polymerization and Ink FormulationD50 D95 D50 D95 D50 D95 (After polymer- (After polymer- D50 D95 Oven(Before (Before (After (After ization ization (Ink aged (Ink agedStability- polymer- polymer- polymer- polymer- and formulated andformulated for 7 days at for 7 days at Particle ization) ization)ization) ization) in ink) in ink) 70oC oven) 70oC oven) size changeExample 100 171 103 165 117 181 111 201 D50- 6 5% D95 11% Example 97 17598 165 105 177 110 178 D50 8 5% D95 1% Example 89 173 104 203 106 214 99212 D50- 10 7% D95- 1% Compa- 101 159 93 169 113 175 113 190 D50 rable0% Example D95 2 9% The Inventive inks show good particle size stabilitywhich is a measure of ink stability.The selected inks were printed and performance parameters evaluated.

TABLE 4 Jetting, Print Properties, Ink Properties Durability DurabilityOD (Brochure OD (Epson (Epson Ink paper) (Brochure Photo Photo InkViscosity Jetting¹⁾ mOD paper) Glossy) Glossy) Conductivity (cP) Example6 0     15 (1x) 1.88 0 (1x) 2.19 0.846 4.86 1 (10 p)  90 (2x) 0 (2x) 4(20 p) 8 (30 p) Example 8 0    105 (1x) 1.8 20 (1x) 2.04 1.622 4.41 0(10 p) 275 (2x) 40 (2x) 0 (20 p) 0 (30 p) Example 10 0     0 (1x) 1.33  0 (1x) 1.6 1.513 3.63 1 (10 p)  60 (2x) 55 (2x) 3 (20 p) 6 (30 p)Comparable 0      0 (1x), 1.87 10 (1x) 2.2 1.74 6 Example 2 1 (10 p)  40(2x) 15 (2x) 1 (20 p) 1 (30 p) The inventive inks performed well in thejettability tests, Durability on two different papers and the OD on thetwo papers were excellent.

What is claimed is:
 1. An inkjet ink comprising an aqueous ink jetvehicle and an aqueous pigment dispersion, wherein said aqueous pigmentdispersion is an encapsulated pigment dispersion which is prepared bythe steps of: a) dispersing a pigment using a polymeric dispersant in anaqueous vehicle wherein the polymeric dispersant not bound to thepigment is less than 0.12 grams per gram of pigment in the pigmentdispersion, and the polymer dispersant bound to the pigment is less than0.33 grams per gram of pigment, where the polymeric dispersant not boundto the pigment is measured by a centrifugation method and is not removedfrom said pigment dispersion before said pigment dispersion isformulated into said ink; b) adding at least one encapsulation monomerto the aqueous vehicle of step (a) to form a first dispersedpigment/encapsulation monomer/aqueous mixture and wherein theencapsulation monomer comprises acrylate monomers; c) dispersing theencapsulation monomer/aqueous mixture using high shear mixing to form asecond dispersed pigment/encapsulation monomer/aqueous mixture; and d)polymerizing the encapsulation monomer by adding a polymerizationinitiator to the second dispersed pigment/encapsulation monomer/ aqueousmixture, wherein for the final encapsulated pigment dispersion theweight ratio of final free polymer to bound polymer is less than 0.9 andthe final free polymer is measured by a density gradient centrifugationmethod; and wherein said polymeric dispersant is crosslinked after thepigment is dispersed and before the encapsulation monomer is added. 2.The inkjet ink of claim 1, wherein the weight ratio of free polymer topolymer bound in the final encapsulated pigment is less than 0.75 asmeasured by the density gradient centrifugation method.
 3. The inkjetink of claim 1, wherein the weight ratio of free polymer to polymerbound in the final encapsulated pigment is less than 0.60 as measured bythe density gradient centrifugation method.
 4. The inkjet ink of claim1, wherein the polymeric dispersant not bound to the pigment is lessthan 0.1 grams per gram of pigment in the pigment dispersion where thepolymeric dispersant is measured by a centrifugation method; and theweight ratio of free polymer to polymer bound to the final encapsulatedpigment is less than 0.6 as measured by the density gradientcentrifugation method.
 5. The inkjet ink of claim 1, wherein the weightratio of encapsulation monomer to pigment is from 0.1 to
 10. 6. Theinkjet ink of claim 1, wherein the weight ratio of encapsulation monomerto pigment is from 0.15 to
 5. 7. The inkjet ink of claim 1, wherein theweight ratio of encapsulation monomer to pigment is from 0.25 to
 1. 8.The inkjet ink of claim 1, wherein the final free polymer bound to thefinal encapsulated pigment is less than 0.25 grams per gram of pigmentas measured by the density gradient centrifugation method.
 9. The inkjetink of claim 1, wherein the polymeric dispersant is selected from thegroup consisting of acrylic dispersant comprising acrylic and acrylatemonomers and polyurethane dispersant and mixtures thereof.
 10. Theinkjet ink of claim 1, wherein the polymeric dispersant is substitutedwith crosslinkable moieties where the crosslinkable moieties areselected from the group consisting of acetoacetoxy, acid, amine, epoxy,hydroxyl, blocked isocyanates and mixtures thereof.
 11. The inkjet inkof claim 10, wherein the polymeric dispersant substituted withcrosslinkable moieties is reacted, after step (a), with a crosslinkingagent where the crosslinking agent has functional groups selected fromacetoacetoxy, acid, amine, anhydride, epoxy, hydroxyl, isocyanates,blocked isocyanates and mixtures thereof.
 12. The inkjet ink of claim 1,wherein the encapsulation monomer is selected from the group consistingof benzyl methacrylate, butyl methacrylate, methyl methacrylate, ethylmethacrylate, propyl methacrylate, hexyl methacrylate, 2-ethylhexylmethacrylate, octyl methacrylate, lauryl methacrylate, stearylmethacrylate, phenyl methacrylate, phenoxyethyl methacrylate,methacrylonitrile, glycidyl methacrylate, p-tolyl methacrylate, sorbylmethacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butylacrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, laurylacrylate, stearyl acrylate, phenyl acrylate, phenoxyethyl acrylate,glycidyl acrylate, p-tolyl acrylate, sorbyl acrylate,ethoxytriethyleneglycol methacrylate, 2-(2-ethoxyethoxy) ethyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-ethoxyethylmethacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, di- andtri-methacrylates, and mixtures thereof.
 13. The inkjet ink of claim 1,wherein the encapsulation monomer further comprises an acrylichydrophilic monomer that is at most 20 weight percent of the acrylatemonomer.
 14. The inkjet ink of claim 13, wherein the acrylic hydrophilicmonomer is selected from the group consisting of methacrylic acid,acrylic acid, maleic acid, maleic acid monoester, itaconic acid,itaconic acid monoester, crotonic acid, crotonic acid monoester,N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate,N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate,t-butylaminoethyl methacrylate, t-butylaminoethyl acrylate and mixturesthereof.
 15. The inkjet ink of claim 1, wherein the encapsulationmonomer further comprises at least one vinyl monomer which is at most 50weight percent of the acrylate monomer, said vinyl monomer is selectedfrom the group consisting of styrene, alpha-methyl styrene, substitutedstyrenes, N-alkyl acrylamides, N-alkyl methacrylamides, vinyl acetate,vinyl butyrate, vinyl benzoate, and mixtures thereof.
 16. The inkjet inkof claim 1, wherein the polymeric dispersant is a structured polymericdispersant selected from the group consisting of block polymerdispersant, branched polymer dispersant, graft star polymer dispersant,and mixtures thereof.